There has recently been a push for the deployment of so-called “small cells” in wireless networks. Small cells are low-powered versions of traditional cells or macrocells. Examples of small cells include femtocells, picocells, and microcells. As demand for bandwidth has increased, small cells provide a way for network operators to offload some of their broadband traffic. Sharing traffic among small cells and macrocells adds a layer of complexity to wireless communication, however. For example, wireless terminals need to have multiple transmitters to communicate with both small cells and macrocells because small cells and macrocells typically communicate on different parts of the radio spectrum.
In current implementations of the Long-Term Evolution (“LTE”) set of standards, when a wireless terminal receives data on a downlink subframe, it transmits an Acknowledgement or Non-Acknowledgement (“ACK” or “NACK”) of those data using an uplink subframe that is no more than four subframes later than the downlink subframe. Each ACK or NACK is spread over two slots of the uplink subframe. While this technique may be adequate when the wireless terminal is transmitting using a single frequency, it can impose limitations on dual-use terminals. Dual-use terminals typically have two transmitters: one for communicating with macrocells (on a first frequency) and one for communicating with small cells (on a second frequency). In particular, simultaneous transmissions from the two transmitters tend to cause the transmitters to interfere with one another.